Right now, this adds rain. This can interact with the WaterMod, rising and lowering the water level based on he weight of it. Pres / to open the GUI menu.
Download this mod with the TerraTech Mod Manager
QMM can be found here.
Use the the Setup program in the Installer folder, or copy the Installer folder's contents to your game's install path (for Steam users, it is somthing like C:\Program Files (x86)\Steam\steamapps\common\TerraTech Beta), go to TerraTech*_Data\Managed and run the Manager executable. Whenever the game updates, just run that executable again.